The objectives of this research are to improve our understanding of the mechanisms of metal acquisition by microorganisms in the marine environment. Interest in the mechanisms of acquisition of iron (and other metal ions) by oceanic bacteria derives from the unique transition metal ion composition of the ocean. Iron is a limiting nutrient to marine microorganisms over much of the world's oceans and has now been shown to regulate the global carbon cycle. Results from the last grant period demonstrated that the majority of marine siderophore structures fall within two categories: 1) suites of self-assembling amphiphilic peptide siderophores including the marinobactins, aquachelins, amphibactins, ochrobactins and synechobactins, which are produced by phylogenetically distinct genera of bacteria; and 2) siderophores containing an alpha- hydroxycarboxylic acid moiety (e.g., beta-hydroxyaspartic acid, citric acid) which when coordinated to Fe(lll) are photoreactive, including the ferric complexes of aquachelins, marinobactins, aerobactin, petrobactins, synechobactins and ochrobactins. The hypothesis to be tested is that the amphiphilic character and photoreactivity confer an advantage for microbial growth tailored to the chemical and physical constraints of the ocean. Certain siderophores produced by pathogenic bacteria bear a structural resemblance to the amphiphilic siderophores produced by marine bacteria, including the mycobactins and carboxymycobactins, produced by mycobacteria, such as M. tuberculosis, which caused tuberculosis and acinetoferrin produced by Acinetobacter haemolyticus which causes respiratory disease. Little is known, however, about the importance of the amphiphilic and photoreactive properties of the mycobacterial and acinetobacter siderophores on the disease state. The specific aims of the proposed research are to i) investigate the photoreactivity of the marine ferric siderophores with alpha-hydroxy acid groups, ii) investigate the amphiphilic properties of the suites of marine amphiphilic siderophores, iii)investigate the photoreactivity and amphiphilic effects on iron acquisition by the source bacteria, and iv) isolate and characterize new siderophores produced by selected other marine bacteria.